The present invention claims the benefit of Japanese Patent Application No. 2000-387707, filed Dec. 20, 2000, the entirety of which is hereby incorporated by reference.
1. Field of the Invention:
The present invention relates to a V-type internal combustion engine having a breather apparatus for recirculating blowby gas from a crankcase to an intake system. In particular, the present invention relates to the arrangement of a breather path constituting the breather apparatus.
2. Description of Background Art:
A V-type internal combustion engine having a breather apparatus for recirculating blowby gas to an intake system has been disclosed in Japanese Utility Model Publication No. 7209/1989. The breather apparatus is provided with a breather chamber provided at a bottom wall portion of a V-bank. A hole communicates the crankcase with the breather chamber. Furthermore, a communication path is formed at a cylinder wall of the cylinder block for communicating the breather chamber and a valve operating chamber, which is in communication with an intake manifold. Accordingly, blowby gas from the crankcase is recirculated to the intake manifold via the breather chamber, the communication path and the valve operating chamber.
In addition, according to the conventional breather apparatus, the communication path, which is also a breather path for flowing blowby gas, is formed in the cylinder wall on an inner side of the V-bank. Therefore, a flow path area of the communication path is limited. Accordingly, in order to ensure a sufficient flow path area, a plurality of communication paths are formed. Alternatively, in order to increase the flow path area of the communication path, it is necessary to significantly bulge the cylinder wall formed with the communication path toward the inner side of the V-bank. Therefore, a width of the bank formed with the communication path is increased in a direction orthogonal to a direction of arrangement of the cylinders, increasing the size of the cylinder block and restricting the arrangement of an intake apparatus in a space formed by the V-bank. Accordingly, the internal combustion engine is increased in size
The present invention has been carried out in view of such a situation and it is an object thereof to provide a V-type internal combustion engine capable of forming a breather path having a sufficiently large flow path area without enlarging the cylinder block.
According to a first aspect of the present invention, a V-type internal combustion engine includes a breather apparatus for recirculating blowby gas from a crankcase to an intake system. A crankshaft having three or more crankpins includes a first, a second and a third crankpin contiguous with each other in a direction of a rotational axis line thereof. A cylinder block is formed with a first and a second bank which form a V-like shape. The first and the third crankpins are respectively connected with a first and a third connecting rod, respectively connected to a first and a third piston, respectively fitted to a first and a third cylinder bore formed at the first bank. The second crankpin is disposed between the first and the third crankpins, is connected only with a second connecting rod, connected to a second piston, fitted to a second cylinder bore formed at the second bank. Furthermore, the breather apparatus includes a breather path formed at a space portion between the first and the third cylinder bores in the first bank.
According to the first aspect of the present invention, in the first bank, the space portion formed between the first and the third cylinder bores which constitutes a position opposed to the second cylinder bore of the second bank, is provided with a minimum width in the direction of the rotational axis line to a degree slightly smaller than a diameter of the second cylinder bore. Therefore, a flow path area of the breather path formed at the space portion can be sufficiently increased without increasing a width of the first bank in the direction of the rotational axis line and a width in a direction orthogonal to an assumed plane including the rotational axis line and a center line of the first cylinder bore or the third cylinder bore. Accordingly, a width of the cylinder block in the direction of the rotational axis line is not increased.
As a result, in the first bank, the breather path is formed at the space portion having a minimum width in the direction of the rotational axis line to the degree slightly smaller than the diameter of the second cylinder bore. Therefore, the breather path having a sufficiently large flow path area is provided without enlarging the first bank in the direction of the rotational axis line and in the direction orthogonal to the assumed plane. Accordingly, the cylinder block is not enlarged and the weight of the cylinder block is reduced. Furthermore, by increasing the flow path area of the breather path, a flow rate of blowby gas flowing through the breather path can be kept to a minimum. Therefore, separation of lubricating oil mist mixed in the blowby gas is expedited.
According to a second aspect of the present invention, there is provided a V-type internal combustion engine having an odd number of cylinders including a breather apparatus for recirculating blowby gas from a crankcase to an intake system. A crankshaft having a plurality of crankpins includes a first and a second crankpin contiguous with each other in a direction of a rotational axis line thereof. A cylinder block is formed with a first bank having an odd number of cylinders and a second bank having an even number of cylinders which form a V-like shape. The first crankpin is connected with a first and a second connecting rod, respectively connected to a first and a second piston, respectively fitted to a first and a second cylinder bore, respectively formed at the first and the second banks. The second crankpin is connected only with a third connecting rod, connected to a third piston, fitted to a third cylinder bore, formed in a bank having a larger number of the cylinders. The breather apparatus includes a breather path formed at a space portion contiguous with the same side at which the second crankpin is contiguous to the first crankpin relative to the first cylinder bore in the bank having a smaller number of the cylinders.
According to the second aspect of the present invention, in the bank having the smaller number of the cylinders, the space portion contiguous with the first cylinder bore or the second cylinder bore disposed at a position opposed to the third cylinder bore of the bank having the larger number of the cylinders, is provided with a width in the direction of the rotational axis line to a degree slightly smaller than a diameter of the third cylinder bore within a range such that the bank having the smaller number of cylinders does not project to the bank having the larger number of the cylinders in the direction of the rotational axis line. A flow path area of the breather path formed at the space portion can sufficiently be increased without increasing a width of the bank having the smaller number of the cylinders in a direction orthogonal to an assumed plane including the rotational axis line and a center line of the first cylinder bore or the second cylinder bore. Accordingly, a width of the cylinder block in the direction of the rotational axis line is not increased. Furthermore, the width in the direction of the rotational axis line is reduced by coupling the two connecting rods to the first crankpin.
As a result, in the bank having the smaller number of cylinders, the breather path is formed at the space portion having the width in the direction of the rotational axis line to a degree slightly smaller than the diameter of the third cylinder bore within the width in the direction of the rotational axis line of the bank having the larger number of cylinders. Therefore, a breather path having a sufficiently large flow path area is provided without enlarging the bank having the smaller number of cylinders in the direction orthogonal to the assumed plane including the rotational axis line and the center line of the cylinder bore. Accordingly, the advantage of the cylinder block being downsized by coupling the two connecting rods to the first crankpin is not deteriorated. Furthermore, by increasing the flow path area of the breather path, a flow rate of blowby gas flowing in the breather path can be kept to a minimum and therefore, the separating of lubricating oil mist mixed in the blowby gas can be expedited.
According to a third aspect of the present invention, there is provided the V-type internal combustion engine according to the second aspect of the present invention, wherein the crankshaft includes a third crankpin contiguous with a side opposed to the side at which the first crankpin is contiguous with the second crankpin. The third crankpin is connected with a fourth and a fifth connecting rod, respectively connected to a fourth and a fifth piston, respectively connected to a fourth and fifth cylinder bore, respectively formed at the first and the second banks. Furthermore, the space portion is present between the first and the fourth cylinder bores or between the second and the fifth cylinder bores.
According to the third aspect of the present invention, in the bank having the smaller number of cylinders, the space portion formed between the first and the fourth cylinder bores or between the second and the fifth cylinder bores, is provided with a minimum width in the direction of the rotational axis line to a degree slightly smaller than the diameter of the third cylinder bore and within the range of a width of the bank having the larger number of cylinders in the direction of the rotational axis line. Therefore, the flow path area of the breather path formed at the space portion can be sufficiently increased without increasing the width of the bank having the smaller number of cylinders in the direction of the rotational axis line and accordingly, without increasing the width of the cylinder block in the direction of the rotational axis line, the width in the direction of the rotational axis line being reduced by coupling the two connecting rods to each of the first and the third crankpins.
As a result, in addition to the advantages according to the second aspect of the present invention, a breather path having a sufficiently large flow path area is provided without enlarging the bank having the smaller number of cylinders in the direction of the rotational axis line and accordingly, without deteriorating the advantage of the cylinder block being downsized by coupling the two connecting rods to each of the first and the third crankpins. Furthermore, the weight of the cylinder block is reduced.
According to a fourth aspect of the present invention, in the V-type internal combustion engine according to any one of the first through third aspects of the present invention, the space portion is formed with a return path for lubricating oil and a partition wall is provided between the breather path and the return path such that the breather path and the return oil path are in parallel with each other in the direction of the rotational axis line.
According to the fourth aspect of the present invention, the space portion is provided with a minimum width in the direction of the rotational axis line to a degree slightly smaller than the diameter of the cylinder bore within a range such that the bank having the smaller number of cylinders does not project to the bank having the larger number of cylinders in the direction of the rotational axis line. In addition, the return path for lubricating oil having a sufficiently large flow path area can be formed in addition to the breather path having a sufficient blow path area without enlarging the cylinder block. Furthermore, the blowby gas and the lubricating oil can be prevented from mixing together by the partition wall, which partitions the breather path and the return oil path to be in parallel with each other in the direction of the rotational axis line.
As a result, the breather path and the return oil path are formed at the space portion having a minimum width in the direction of the rotational axis line to a degree slightly smaller than the diameter of the cylinder bore such that they do not project in the direction of the rotational axis line relative to the bank having the larger number of cylinders. Accordingly, the return oil path having a sufficient flow path area is provided along with the breather path without enlarging the cylinder block and the lubricating oil therefore returns smoothly. Furthermore, the blowby gas and the lubricating oil can be prevented from mixing together by the partition wall and an amount of the lubricating oil mist mixed into the blowby gas can be reduced.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.